This invention relates to creating and updating a process capability database including the collection of expert knowledge, which database is used by design engineers in the course of designing and manufacturing parts or features of parts that are quality controlled preferably using a six sigma quality control regime.
Process capability refers to the accuracy or tolerance by which a manufacturing process can fabricate parts or features of parts. Process capability information is crucial to the quality design of products that depend on these parts and features. Known procedures allow calculation of process capability via careful measurement of features manufactured by the process. This is a time consuming process which, when properly done, requires measurement over a number of potentially confounding variables such as time of day, day of week, shift, environment, etc. When a manufacturing firm develops a wide variety of products, a significant effort must be expended before quality design procedures can be employed.
In an effort to streamline process capability knowledge, there has been employed the use of xe2x80x9cexpertxe2x80x9d knowledge to augment existing sources of information relating to process capability. For example, Zucherman (SME paper MS86-951, xe2x80x9cA Knowledge Base Development for Producibility Analysis in Mechanical Designxe2x80x9d) describes the use of an expert system to analyze a design from a producibility standpoint. However, this document does not describe the acquisition of process capability data and/or any subsequent manipulation of that acquired data to properly populate a database used for assessing process capability.
U.S. Pat. No. 5,452,218 to Tucker et al. describes a system and method for determining quality analysis on fabrication and/or assembly design using shop capability data. In the scheme disclosed by Tucker et al., which is applicable to a six sigma quality model, there is an opportunity to consult with a process consultant with respect to information not found in a previously prepared database. However, except for noting that consultation can be effected via e-mail or electronic message, Tucker et al. do not address any details regarding the input of expert information into a database, or the desirability of any particular manipulation of the obtained information that is input, especially in view of a six sigma quality control approach.
It is therefore desirable to provide a procedure and method for eliciting expert opinion on process capability and thereafter manipulating the elicited information in such a manner that it can effectively be used to populate a process capability database, operating in a six sigma regime, that is accessed by at least design and process engineers. The manipulation preferably includes converting the expert elicited information from a tolerance-type metric to a short term standard deviation (or sigma) metric, whereby the result of the manipulation is used to populate directly a process capability database and, as appropriate, thereby augment, replace or modulate the data already stored therein.
With this method, the knowledge of experienced manufacturing and design engineers can rapidly fill a process capability database for a large number of parts and features across multiple processes. This provides not only a basis for quality design, but an initial benchmark for process improvement.